The present invention relates to a hand welding device for short-time arc welding of elements, such as metal studs, to parts, such as metal sheets, having a handlable housing, a holding means mounted on the housing to hold an element to be welded onto a part, a reciprocating means mounted on the housing for setting and resetting the holding means relative to the housing, and positioning means mounted on the housing to maintain a predetermined distance from the part.
The present invention relates further to a welding apparatus having a part, such as a metal sheet, a hand welding device holding an element, such as a metal stud, to be welded onto the part, and a welding gauge fastened to the part, said hand welding device comprising positioning means for maintaining a predetermined distance from the part. Finally, the present invention relates to a welding gauge for positioning a hand welding device on a part, such as a metal sheet. Such hand welding devices for short-time arc welding are universally known.
In short-time arc welding (also known as stud welding) elements such as metal studs are welded onto metal parts such as metal sheets. The studs serve as anchors for various fastening purposes. Accordingly, the studs may be configured as threaded studs (with metric thread), as coarse-threaded studs, pine tree studs, T-studs, etc. In the automotive industry, stud welding has been much used for some years. Here the stud welding technology serves to fasten body parts, to lay electric leads, to fasten carpeting, etc. Predominantly, in the automotive industry, robots are employed to achieve high productivity where a stud welding unit is fastened to the end of a robot arm. The stud welding unit is connected to an electrical energy supply and to an automatic stud feeding device.
In the automotive industry, the so-called stroke ignition process is especially used. Here a metal stud is first placed in the location on the metal sheet where it is to be welded on. Then a so-called pilot current is switched on and the metal stud is lifted somewhat relative to the metal sheet. Thus an electric arc is set. Then the welding current proper is switched on and the mutually opposed faces are incipiently fused by the high-energy electric arc. Then the metal stud is again lowered onto the metal sheet so that the respective melts will mingle. The arc is short-circuited. The combined melt solidifies and the welding operation is complete.
In the case of robot-supported stud welding units, the approach to the welding position and the moving of the metal stud are automated by means of a reciprocating device. Especially the reciprocating motions of the metal stud relative to the metal sheet are very small (millimeter range). To obtain consistently good welding results, it is important that the stud welding unit be always exactly positioned relative to the metal sheet and that the stroke of the reciprocating device is always exactly maintained.
Besides the robot-supported stud welding units, there are also hand welding devices for stud welding. The known hand welding devices also comprise a holding device for holding one metal stud at a time and a reciprocating device for advancing and resetting the holding device, and with it the metal stud relative to a housing of the hand welding device. To achieve consistently good welding results, it is indispensable that positioning means be provided, serving to keep the distance to the part constant.
As a rule, hand welding devices comprise one or more supporting feet for this purpose, extending parallel to the holding means. Alternatively, there are also so-called nozzles, of tubular configuration and surrounding the holding means. Before a welding operation is initiated, the supporting feet, or the nozzle, are set on the part or metal sheet. Then the reciprocating device is first actuated to place the metal studs on the sheet metal. Then the pilot current is switched on, the arc is set, and the welding operation proper is completed. Alternatively, the reciprocating means is pre-stressed so that the holding device stands slightly ahead on the metal sheet before the stud is placed. In the welding position, the stud and the anterior end of the supporting foot or nozzle lie in contact with the metal sheet. The supporting foot or the nozzle thus always maintains an exact relative position between the hand welding device or its housing and the metal sheet.
The supporting foot and/or the nozzle extend parallel to the centerline, essentially as far as the anterior end of the holding means. This is essentially unproblematical in the case of plane metal sheets. However, there are applications in which metal studs are to be welded onto curved surfaces. With close radii of curvature in the area of the weld, it may happen that the supporting foot and/or the nozzle come into contact in the area of curvature. Consequently there is the wrong distance between the metal stud and the metal sheet before the welding operation proper is begun. This may lead to problems in terms of quality of the welding operation.
Here a single supporting foot is still advantageous inasmuch as suitable rotation can be found between hand welding device and metal sheet, possibly a position in which the supporting foot rests in contact with a plane area. With several supporting feet and/or the nozzle, this possibility is not available. With a single supporting foot, however, there is great danger that the hand welding device may be held oblique relative to the metal sheet, and this too may impair the quality of the weld.
Motor vehicle models are often fabricated in different places. In some places, there are robots prepared for stud welding. In other places, welding must be done by hand. The bodywork parts, however, are in all cases the same. Therefore the bodywork designer must so choose the location of studs to be welded on that welding by hand is possible. Here the designer is at present limited to places where no unduly sharp curvatures are present. In the case of fabrication in places with no robot support, and for small series or in repair work, it is known that a welding gauge may be fastened to the part or metal sheet. The welding gauge serves to weld the metal stud exactly in the desired place. For this purpose the hand welding device may be guided to the welding gauge parallel to the centerline in order thereby to fix the location of the weld.
The welding gauge is as a rule fixed to the metal sheet at a distance therefrom, and comprises an opening. In the case of the hand welding device with nozzle, the opening is of circular configuration. The diameter of the opening is adapted to the outside diameter of the nozzle, so that the hand welding device is guided by means of the nozzle.
Against the background of the above mentioned prior art, the object of the present invention is to specify an improved hand welding device, an improved welding apparatus and an improved welding gauge. In the hand welding device initially mentioned, this object is accomplished in that the positioning means are offset to the rear relative to the anterior end of the holding means, so that the positioning means are able to bear on a welding gauge fixed to the part in order to maintain the predetermined distance. Finally, the above object is accomplished by a welding gauge for positioning a hand welding device on a part, such as a metal sheet, having an opening through which a holding means of the hand welding device can be passed to the part in order to weld an element, such as a metal stud, to the part, and at least one stop adjustable upward against which the positioning means of the hand welding device can be set, in order to maintain a predetermined distance of the hand welding device from the part.
By maintaining the correct distance between the hand welding device and the part, or metal sheet, in that the housing of the hand welding device, or positioning means provided thereon, act directly on the welding gauge and do not contact the part itself at all, welding operations can be performed also in the area of curved locations. The positioning means, in all operating conditions and particularly in the welding position, are offset to the rear relative to the anterior end of the holding means.
The welding gauge is rigidly mounted on the part and itself has sufficient rigidity to ensure an exact positioning. Consequently, a supporting foot extending parallel as far as the anterior end of the holding means, or a corresponding nozzle, may be dispensed with. Consequently, welding operations may be performed even where the surface of the part is extremely curved in the immediate neighborhood. Consequently the bodywork designer has greater degrees of freedom in the arrangement of places where the studs are to be welded on. In this way, expense can be saved even at the design level.
For the welding gauge according to the invention, it is of advantage that the stop against which the positioning means of the hand welding device can be set be adjustable in height. The welding gauge according to the invention in fact does not serve only for correct guidance of the hand welding device on its way to the correct weld location. It also serves to fix the distance of the hand welding device from the part. Owing to the adjustability of the stop, there is the possibility here of adjusting the welding gauge exactly and/or adapting it to different applications.
In the hand welding device according to the invention, it is advantageous if the positioning means comprise at least one pin extending essentially parallel to the direction of action of the holding means. In this way, an exact positioning can be realized, particularly in an axial direction, with little engineering outlay on the hand welding device.
It is especially preferred if the positioning means comprise two positioning elements, in particular two pins. With two pins, the position of the hand welding device can be exactly oriented laterally as well, and to a large extent, the manual welding device can be prevented from approaching the part obliquely. One or two pins will not indeed serve to achieve perfect tilting stability as this requires three pins. It has been found, however, that even with only one pin, better with two pins, it is possible for the user to position the hand welding device essentially perpendicular in relation to the part if the welding gauge provides sufficient axial guidance. Here it is of especial advantage if the two pins and the centerline lie at the vertices of an equilateral triangle, to which the axis is perpendicular. This symmetry results in a high stability over all.
According to a further proposal of the invention, provision may be made that the positioning means comprise three positioning elements, in particular pins, the end points of the positioning elements lying at the vertices of a triangle. By this conformation, stable support of the hand welding device on the welding gauge is assured, and so is an exact orientation of the centerline with the part. The element to be welded onto the part may therefore be welded to the part with great precision as to position and angle. Another advantage of this conformation is that an axial guidance on the welding gauge may be dispensed with, so that the mounting of the hand welding device on the welding gauge and its removal therefrom is facilitated, thus simplifying handling.
In the welding apparatus according to the invention, it is of advantage if the welding gauge comprises support means for the positioning means, which support means may be designed to guide the positioning means axially, in order thus to fix the weld location. The support means serve firstly to maintain the predetermined distance and secondly to perform the actual function of the welding gauge, namely to fix the weld location in the plane of the part. Advantageously, the support means of the welding gauge comprise at least two depressions, one positioning element acting in each depression, to be oriented therein. With two depressions, the position of the hand welding device on the welding gauge can be uniquely determined. If a third positioning element is present, it requires support in axial direction only.
If the hand welding device comprises three pins for support on the welding gauge, then according to a further proposal of the invention, the application and removal of the hand welding device may be facilitated in that the depressions comprise an opening narrowing down towards the bottom. Consequently the welding gauge can be realized economically. Here it is of special advantage if the welding gauge comprises an opening for the holding means, the cross-section of the opening being essentially greater than the cross-section of the holding means. Contrary to conventional welding gauges, therefore, the opening for the holding device no longer has any guidance function. In this way it is more readily possible to inspect the part visually prior to the welding operation.
According to another preferred embodiment, the welding gauge comprises support means for the positioning means, said support means comprising means for adjusting the distance. The support means as a rule comprise one or more stops, adjustable in height. In this way it is possible to optimize the welding gauge for the current weld location and operation and to make readjustments. The features mentioned above, and the features yet to be illustrated, may be employed not only in the particular combination specified, but also in other combinations or alone.